U.S. patent application number 15/538662 was filed with the patent office on 2017-12-28 for fast response active reactive power (kvar) compensator.
The applicant listed for this patent is Edge Electrons Limited. Invention is credited to Wing Ling CHENG, Neal George Stewart.
Application Number | 20170373499 15/538662 |
Document ID | / |
Family ID | 56355535 |
Filed Date | 2017-12-28 |
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United States Patent
Application |
20170373499 |
Kind Code |
A1 |
Stewart; Neal George ; et
al. |
December 28, 2017 |
FAST RESPONSE ACTIVE REACTIVE POWER (KVAR) COMPENSATOR
Abstract
Legacy automatic variable capacitor KVAR compensation systems
typically use either electromechanical devices such as relays or
contactors of various forms and types to switch the selected
capacitors in and out of the electrical system under some form of
electronic control. These systems are slow and discontinuous in
their ability to closely regulate the exact value of compensatory
capacitance needed to compensate the variable and rapidly changing
reactive power KVAR in the electrical power transmission and
distribution networks. The present invention provides a fast
response active KVAR compensator based on a variable transimpedance
topology.
Inventors: |
Stewart; Neal George; (Hong
Kong, HK) ; CHENG; Wing Ling; (Hong Kong,
HK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Edge Electrons Limited |
Hong Kong |
|
HK |
|
|
Family ID: |
56355535 |
Appl. No.: |
15/538662 |
Filed: |
January 6, 2016 |
PCT Filed: |
January 6, 2016 |
PCT NO: |
PCT/CN2016/070254 |
371 Date: |
June 22, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62100074 |
Jan 6, 2015 |
|
|
|
62100076 |
Jan 6, 2015 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02J 3/1814 20130101;
Y02E 40/18 20130101; H02M 5/04 20130101; H02J 3/18 20130101; Y02E
40/10 20130101 |
International
Class: |
H02J 3/18 20060101
H02J003/18; H02M 5/04 20060101 H02M005/04 |
Claims
1. A reactive power (KVAR) compensator for compensating leading or
lagging KVAR in alternating current (AC) distribution systems, the
KVAR compensator comprising: a first and a second independently
controllable AC bidirectional switches; a first power inductor; a
first current transformer for generating a first power inductor
current direction data signal indicating the first power inductor
current direction; an output capacitor with a fixed capacitance or
an output inductor with a fixed inductance; and a control circuitry
for receiving an AC input voltage, an AC output voltage, and the
first power inductor current direction data signal, measuring a
KVAR value, and setting a variable gain to generate an apparent
impedance across the AC input for compensating the KVAR.
2. A reactive power (KVAR) compensator for compensating leading or
lagging KVAR in alternating current (AC) distribution systems, the
KVAR compensator comprising: a first unipolar paths, comprising: a
first half-bridge, comprising a first and a second rectifiers
connected in series with a first and a second independently
controllable unipolar switches respectively, a first power
inductor, and a first current transformer for generating a first
power inductor current direction data signal indicating the first
power inductor current direction; a second unipolar paths,
comprising: a second half-bridge, comprising a third and a forth
rectifiers connected in series with a third and a forth
independently controllable unipolar switches respectively, a second
power inductor, and a second current transformer for generating a
second power inductor current direction data signal indicating the
second power inductor current direction; an output capacitor with a
fixed capacitance or an output inductor with a fixed inductance;
and a control circuitry for receiving an AC input voltage signal,
an AC output voltage signal, the first power inductor current
direction data signal, and the second power inductor current
direction data signal, measuring a KVAR value, and setting a
variable gain to generate an apparent impedance across the AC input
for compensating the KVAR.
3. A reactive power (KVAR) compensator for compensating leading or
lagging KVAR in alternating current (AC) distribution systems, the
KVAR compensator comprising: a first unipolar paths, comprising: a
first half-bridge, comprising a first and a second unipolar
switching devices, a first power inductor, and a first current
transformer for generating a first power inductor current direction
data signal indicating the first power inductor current direction;
a second unipolar paths, comprising: a second half-bridge,
comprising a third and a forth unipolar switching devices, a second
power inductor, and a second current transformer for generating a
second power inductor current direction data signal indicating the
second power inductor current direction; an output capacitor with a
fixed capacitance or an output inductor with a fixed inductance;
and a control circuitry for receiving an AC input voltage signal,
an AC output voltage signal, the first power inductor current
direction data signal, and the second power inductor current
direction data signal, measuring a KVAR value, and setting a
variable gain to generate an apparent impedance across the AC input
for compensating the KVAR.
Description
CROSS REFERENCE OF RELATED APPLICATION
[0001] The present application is a national phase application of
the international patent application PCT/CN2016/070254 filed on
Jan. 6, 2016 which claims priority to the U.S. Provisional Patent
Application No. 62/100,074, filed Jan. 6, 2015, and U.S.
Provisional Patent Application No. 62/100,076, filed Jan. 6, 2015,
the disclosures of which are incorporated herein by reference in
their entirety.
FIELD OF THE INVENTION
[0002] The present invention generally relates to electrical power
generation and distribution. Particularly, the present invention
relates to methods and devices for alternating current (AC)
reactive power (KVAR) compensation in AC electrical power
generation and distribution.
BACKGROUND
[0003] In AC electrical power distribution networks, the optimized
operating conditions for maximum energy efficiency in the usage,
transmission, and delivery of AC electrical power is when the
voltage and the current are closely in phase, and the reactive
power (KVAR) is close to zero. However, with the addition of
reactive loads and inherent reactive components such as capacitance
and inductance in the transmission and distribution system, the AC
current in the system can be phase-shifted with respect to the
voltage waveform. This creates power quality issues that affect the
efficient transmission and usage of the delivered electrical power.
The degradation in power quality due to the increasing reactive
power value is measured by the amount of phase angle shift of the
current behind (lagging) or ahead (leading) with respect to the
voltage waveform. Reactive power value is derived by the following
equation.
KVAR= {square root over (KVA.sup.2-KW.sup.2)} (1)
where KVAR is the total reactive power, KVA is the total apparent
power, and KW is real power.
[0004] Noted that only the real power KW is useful for productive
consumption, whereas the reactive power KVAR is wasted power. But
since the total apparent power KVA is made up of KW and KVAR as per
the equation above, both power components are be generated,
transmitted, and delivered. As such, an increasing phase shift of
the AC current with respect to the voltage waveform, which means
increasing value of reactive power KVAR will translate into a
significant efficiency decrease in the electrical power system.
[0005] This problem is well known and there are various legacy
methods of compensating and removing reactive power KVAR by
introducing reactive components at various points within the
electrical system. Typically these are capacitors introduced in
shunt across the electricity supply lines to cancel the generally
lagging current due to magnetic elements such as electric motors,
fluorescent ballasts, transformers, etc.
[0006] This has been traditionally achieved by adding fixed and
variable capacitor banks in shunt across the electrical power
transmission and distribution system. If a known and reproducible
KVAR problem is stable, then a fixed capacitor KVAR compensation
bank can be permanently installed at the point to be compensated.
If the reactive power KVAR is changing, then automatic variable
capacitor banks that can respond, under electronic controls and
KVAR sensing, and switch in the amount of capacitance needed to
compensate for the level of KVAR at any given time.
[0007] These legacy automatic variable capacitor KVAR compensation
systems typically use either electromechanical devices such as
relays or contactors of various forms and types to switch the
selected capacitors in and out of the electrical system under some
form of electronic control. In more recent versions of KVAR
compensation systems, semiconductor switching devices, such as
triodes for alternating current (TRIACs) and silicon-controlled
rectifiers (SCRs), and electromechanical switching devices have
been seen in use.
[0008] Because of the need to switch discrete component capacitors
in and out of circuit by various switching means, these legacy
reactive power KVAR compensators are slow and discontinuous in
their ability to closely regulate the exact value of compensatory
capacitance needed to compensate the variable and rapidly changing
reactive power KVAR in the electrical power transmission and
distribution networks.
SUMMARY
[0009] In addressing the abovementioned shortcoming of the legacy
automatic variable capacitor KVAR compensation systems, the present
invention provides a fast response active KVAR compensator. In
various embodiments in accordance to the present invention, the
fast response active KVAR compensator is based on a variable
transimpedance topology.
[0010] In one preferred embodiment, the fast response active KVAR
system employs the specific AC variable voltage topology as
described in the U.S. Pat. No. 9,148,058 issued Sep. 29, 2015 and
the same in the PCT International Patent Application No.
PCT/CN2014/089721 filed Oct. 28, 2014; the disclosures of which are
incorporated herein by reference in their entirety. In another
preferred embodiment, the fast response active KVAR system employs
the specific AC variable voltage topology as described in the U.S.
patent application Ser. No. 14/565,444 filed Dec. 10, 2014 and the
same in the PCT International Patent Application No.
PCT/CN2014/093475 filed Dec. 10, 2014; the disclosures of which are
incorporated herein by reference in their entirety.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Embodiments of the invention are described in more detail
hereinafter with reference to the drawings, in which
[0012] FIG. 1 depicts a logical diagram illustrating a general
variable transimpedance topology;
[0013] FIG. 2 depicts a circuit diagram of an embodiment of the
fast response active KVAR compensator in accordance to the present
invention; and
[0014] FIG. 3 depicts a circuit diagram of another embodiment of
the fast response active KVAR compensator in accordance to the
present invention.
DETAILED DESCRIPTION
[0015] In the following description, methods and systems for
compensating reactive power (KVAR) in electrical power generation
and distribution networks and the like are set forth as preferred
examples. It will be apparent to those skilled in the art that
modifications, including additions and/or substitutions may be made
without departing from the scope and spirit of the invention.
Specific details may be omitted so as not to obscure the invention;
however, the disclosure is written to enable one skilled in the art
to practice the teachings herein without undue experimentation.
[0016] FIG. 1 depicts a logical diagram illustrating a general
variable transimpedance topology and it is used herein to show the
general operating principle of a transimpedance system in which the
value of an output impedance (Z.sub.o) across the output 103 of the
alternating current (AC) amplifier 101 is transferred and reflected
onto the input 102 of the AC amplifier. The value of this
transferred input impedance (Z.sub.in) is related the output
impedance (Z.sub.o) by the gain of the controlled gain AC amplifier
(A.sub.v). Thus, if the gain of the AC amplifier (Ag) is
controllable and variable, not only a controlled transimpedance can
be generated across the input 102 from the fixed output impedance
(Z.sub.o) across the output 103, the apparent impedance (Z.sub.in)
across the input 102 can be smoothly and accurately controlled with
a very fast response. The quickness of change of the apparent
impedance (Z.sub.in) across the input 102 is due to the fact that
it only depends upon the response speed of the control
electronics.
[0017] Still referring to FIG. 1. The relationship between the
apparent input impedance (Z.sub.in) and the output impedance
(Z.sub.o) is governed by the following equation.
Z in = 1 Av 2 .times. Z o ( 2 ) ##EQU00001##
In specifying a particular value of the output impedance (Z.sub.o),
either a capacitor across the output 103 with a fixed capacitance
value (C.sub.o) or an inductor across the output 103 with a fixed
inductance value (L.sub.o) can be used. Then, the relationship
between the reflected apparent input capacitance (C.sub.in) and the
output capacitance (C.sub.o) is governed by the following
equation.
C.sub.in=Av.sup.2.times.C.sub.o (3)
And the relationship between the reflected apparent input
inductance (L.sub.in) and the output inductance (L.sub.o) is
governed by the following equation.
L in = L o Av 2 ( 4 ) ##EQU00002##
It can be seen that by varying the gain of the AC amplifier
(A.sub.v), the apparent value of reflected capacitance (C.sub.in)
or reflected inductance (L.sub.in) at the input of the ac amplifier
can be varied over a range not only continuously without discrete
steps, but also with a very rapid response limited only by the
response speed of the control electronics.
[0018] FIG. 2 depicts a circuit diagram of an embodiment of the
fast response active KVAR compensator in accordance to the present
invention. In this first preferred embodiment, the fast response
active KVAR compensator utilizes the buck section with an output
capacitor 203 of fixed capacitance (C.sub.o) across the output of
the AC series buck-boost voltage regulator electronic circuitry
described in the U.S. Pat. No. 9,148,058 and the same in the PCT
International Patent Application No. PCT/CN2014/089721 to achieve
the KVAR compensation function.
[0019] Still referring to FIG. 2. As the gain of the AC variable
voltage topology is changed by the electronic control module 202 in
response to the level of KVAR at the input 201, the value of the
apparent input capacitance (C.sub.in) across the input 201 is
accurately adjusted to compensate and cancel out the reactive power
KVAR. This is done without discrete capacitor steps, thus the
apparent input capacitance (C.sub.in) adjustment is achieved in
smooth and continuous manner, and the response time depends only
upon the response speed of the control electronics of the
electronic control module 202.
[0020] Although it is described here with the preferred embodiment
utilizing the buck section of the AC series buck-boost voltage
regulator electronic circuitry described in the U.S. Pat. No.
9,148,058 and the same in the PCT International Patent Application
No. PCT/CN2014/089721 to achieve the KVAR compensation function, it
should be obvious to an ordinarily skilled person in the art to use
the boost section of the aforesaid AC series buck-boost voltage
regulator electronic circuitry instead of the buck section.
[0021] Also, although it is described here with the preferred
embodiment utilizing a capacitor of fixed capacitance across the
output of the buck section of the AC series buck-boost voltage
regulator electronic circuitry described in the U.S. Pat. No.
9,148,058 and the same in the PCT International Patent Application
No. PCT/CN2014/089721 to compensate for a lagging KVAR, it should
be obvious to an ordinarily skilled person in the art to substitute
the aforesaid capacitor with an inductor of fixed inductance to
compensate for a leading KVAR.
[0022] FIG. 3 depicts a circuit diagram of another embodiment of
the fast response active KVAR compensator in accordance to the
present invention. In this second preferred embodiment, the fast
response active KVAR compensator utilizes the buck section with an
output capacitor 303 of fixed capacitance (C.sub.o) across the
output of the AC series buck-boost voltage regulator electronic
circuitry described in the U.S. patent application Ser. No.
14/565,444 and the same in the PCT International Patent Application
No. PCT/CN2014/093475 to achieve the KVAR compensation
function.
[0023] Still referring to FIG. 3. As the gain of the AC variable
voltage topology is changed by the electronic control module 302 in
response to the level of KVAR at the input 301, the value of the
apparent input capacitance (C.sub.in) across the input 301 is
accurately adjusted to compensate and cancel out the reactive power
KVAR. This is done without discrete capacitor steps, thus the
apparent input capacitance (C.sub.in) adjustment is achieved in
smooth and continuous manner, and the response time depends only
upon the response speed of the control electronics of the
electronic control module 302.
[0024] Although it is described here with the preferred embodiment
utilizing the buck section of the AC series buck-boost voltage
regulator electronic circuitry described in the U.S. patent
application Ser. No. 14/565,444 and the same in the PCT
International Patent Application No. PCT/CN2014/093475 to achieve
the KVAR compensation function, it should be obvious to an
ordinarily skilled person in the art to use the boost section of
the aforesaid AC series buck-boost voltage regulator electronic
circuitry instead of the buck section.
[0025] Also, although it is described here with the preferred
embodiment utilizing a capacitor of fixed capacitance across the
output of the buck section of the AC series buck-boost voltage
regulator electronic circuitry described in the U.S. patent
application Ser. No. 14/565,444 and the same in the PCT
International Patent Application No. PCT/CN2014/093475 to
compensate for a lagging KVAR, it should be obvious to an
ordinarily skilled person in the art to substitute the aforesaid
capacitor with an inductor of fixed inductance to compensate for a
leading KVAR.
[0026] Any ordinarily skilled person in the art can apply the
inventive principles described herein to any poly-phase AC systems,
such as three-phase electrical systems, without departing from the
scope and spirit of the invention.
[0027] The embodiments disclosed herein may be implemented using
general purpose or specialized computing devices, computer
processors, microcontrollers, or electronic circuitries including
but not limited to digital signal processors (DSP), application
specific integrated circuits (ASIC), field programmable gate arrays
(FPGA), and other programmable logic devices configured or
programmed according to the teachings of the present disclosure.
Computer instructions or software codes running in the general
purpose or specialized computing devices, computer processors, or
programmable logic devices can readily be prepared by practitioners
skilled in the software or electronic art based on the teachings of
the present disclosure.
[0028] The foregoing description of the present invention has been
provided for the purposes of illustration and description. It is
not intended to be exhaustive or to limit the invention to the
precise forms disclosed. Many modifications and variations will be
apparent to the practitioner skilled in the art.
[0029] The embodiments were chosen and described in order to best
explain the principles of the invention and its practical
application, thereby enabling others skilled in the art to
understand the invention for various embodiments and with various
modifications that are suited to the particular use contemplated.
It is intended that the scope of the invention be defined by the
following claims and their equivalence.
* * * * *